Xfer case fill hole overflowing (1 Viewer)

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Aug 3, 2012
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Louisville, KY
Hey all.

I just finished a transfer case rebuild about 500 miles ago. Yesterday, I pulled the fill plug on the trans and transfer case as a quick check and had oil pouring out of the transfer case fil hole. The truck has been sitting for apx 3 weeks (if that matters any). I rebuilt with a terrain tamer kit from cruiser bros. If I remember correctly the common result of a damaged or bad transfer to transmission seal is oil pumping from the transfer case into the transmission (not the other way around). It would seem that if the seal was severely failed (or missing) gravity would move fluid from the trans to the transfer. Any other thoughts / actions before I pull the case and inspect?

Scratching my head on this one. If I forgot to put that seal in I may have to just sell the 40;)

Thx.
 
was the transmision low?

just sitting the seal area is above both oil levels. are all the bolts installed holding the transfer to the trans?
 
was the transmision low?

just sitting the seal area is above both oil levels. are all the bolts installed holding the transfer to the trans?
Yes. Trans was low. All bolts are installed. I’m assuming that the seal is gone or missassembled or shot. I’m planning on dropping the fluid level to the right height in the xfer case but leave the plug out. Then fill the transmission to the proper level. If fluid comes out of the transfer case fill hole soon after that then the seal is missing or really damaged.
 
Connect the filling plugs with a hose. I don’t know the english word for this setup.

41B301D9-EB02-4BC8-9327-AE3793C7793D.jpeg
 
Connect the filling plugs with a hose. I don’t know the english word for this setup.

View attachment 2022113
Thx for the suggestion. I don’t think this will help in my situation. The fill hole on the transmission is higher than the transfer case. My transfer case is overflowing not the transmission. The usual failure (that the hose you showed resolve) is when oil is pumped from the transfer case into the transmission past the seal. Mine seems to be draining from the transmission into the transfer case.

It is however possible that if I ran the truck a bit (which I can’t do right now) , oil may move from the transfer case back into the transmission and then when parked, it could slowly drain back into the transfer case. If that is the case, that hose may help.
 
correct on the hose not working for getting oil back into the trans.
leave the transfer empty, fill the trans and leave it for a week or two and see if the oil migrates into the transfer. it is not the seal as the seal is above the oil level. my guess would be either the mounting bolts are not sealed or the idler shaft is not sealed, those are the 2 places to get oil transferred thru from trans to transfer.
 
@3_puppies the idler shaft is not connected to the transmission in any way as far as I understand. It is strictly the output shaft of the transmission and possibly the transfer to transmission mounting bolts I believe. I thought the output shaft seal was below the oils fill line on the transmission. Could be wrong. Will check tomorrow.
 
@3_puppies

1. Pulled the fill plug on the transmission and confirmed it was low (about 1/2 a pinky finger low). Put the fill plug back in.
2. I pulled the fill plug on the transfer case and drained off the extra oil into a clean container. It was probably a 1/2 quart. Then put the fill plug back in.
3. poured all of the oil down the hole for the transmission shifter.
4. Then I pulled fill plug on the transmission and oil came out! Probably 1/4 quart. (Roughly 1/2 of what came out of the transfer case).
5. I took a look at a spare transfer case housing that I had and it looks pretty conclusive that the oil seal for the transmission output shaft is above the fill plug for the transmission. Which means oil should not naturally flow between the transmission and transfer case (even if that seal were missing).

I plan to let the truck sit for a few days or a week and see if oil moves.

It is possible (not exactly sure how) that the trans was always low and the transfer was always overfilled. When I filled them the truck was on a lift. It is possible that if it were not sitting flat but rather the drivers side corner was sitting high and the passengers rear corner was low then the transmission could get underfilled and the transfer case could be overfilled. (That would be great news).
 
It's been awhile since I had a 1 piece transfer case apart, trying to go by memory. the idler shaft has a plug/seal that seals the transmision side of the idler shaft to keep oil separate. only other place I can see oil migrating would be thru the lower mounting bolt.
other thing you could do is to remove the pto cover leave the transfer drained and see if you can see a trail of oil going from the transmision into the transfer.
I doubt the rig not being perfectly level would cause this issue.
 
On the one piece transfer case the only points where oil could migrat between the two would be the shaft seal and the lower connection boots between the trans and case. The idler shaft is has a Welch style plug on one end and an o-ring on the other.

The thought about the truck being out of level was because it was on a lift when filling the cases so the drive train was undoubtedly not at the same angle as it is when on the ground. Also, after draining the case to the proper level and then using that oil to top off the transmission I had 1/4 quart of oil in excess. That could have been caused by the drive train being in a different orientation when I filled it.

We will see:)


Good idea about draining the the case and looking for oil flow through the pto cover.

Appreciate the help!
 
You need to pry the spring-loaded vent cap off your transfer case and install a 3/8" piece of fuel line to the stub (with a hose clamp), and then run the hose up the firewall.

When the transfer case heats and cools, it pulls a vacuum and sucks oil past the seal, and overfills itself. You may have other seal issues, but a plugged xfer case vent is part of your problem. Your transmission naturally vents through the shifter tower, so you need not vent the transmission in any way.
 
@SteveH

Thx for the suggestion. Not the problem in this case. I removed the breather cap after the rebuild so that I could relocate it up the firewall.
 

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